Since we relaxed the assumption of \(f=1\) , the estimate for \(\tau _{\text{0}}\)  does not hold any further. However, as indicated by the resonance line ratios, outside of the reconnection region it is most likely \(<1\) . The possible path lengths are thus determined using the derived linear relation, while their upper boundary is \(\approx \) 2000 km. As it has been demonstrated for flares in stars [1]}
if the electron density in the atmosphere is
known, opacity can provide important information on the linear
dimensions of the scattering layer.
